https://bugs.gentoo.org/540856

respect user CFLAGS

--- a/Makefile.am
+++ b/Makefile.am
@@ -23,7 +23,7 @@ numastat_CFLAGS = $(AM_CFLAGS) -std=gnu99
 
 numademo_SOURCES = numademo.c stream_lib.c stream_lib.h mt.c mt.h clearcache.c clearcache.h
 numademo_CPPFLAGS = $(AM_CPPFLAGS) -DHAVE_STREAM_LIB -DHAVE_MT -DHAVE_CLEAR_CACHE
-numademo_CFLAGS = -O3 -ffast-math -funroll-loops
+numademo_CFLAGS = $(AM_CFLAGS) -ffast-math -funroll-loops
 if HAVE_TREE_VECTORIZE
 numademo_CFLAGS += -ftree-vectorize
 endif
